It is well known that turfs for sports fields such as for soccer, hockey, cricket, rugby, etc. provide a natural turf grown on a ground or substrate. Natural turfs offer high aesthetical, technical and environmental performances.
However, with the use and with time, as well as with unfavourable weather conditions, the natural turf quickly wears and requires expensive maintenance work. Unless a worn natural turf is completely restored, the playing field is anaesthetical, irregular, and potentially dangerous for the users.
An intense activity, which normally concerns a sports field, worsens the turf characteristics after each use without enough time for the turf to recover. In particular, the playing field looses its planarity, uniformity and resistance of its substrates, affecting the athletic performances and endangering the athlets.
For these reasons, synthetic playing fields have been developed in the last years, having artificial grass blades and granular infill material, for example sand or resilient material, which present improved performances and steadiness of grip on the ground. Such artificial turfs can be installed on surfaces that are made of various materials, in particular asphalt, and stabilized inert material.
Artificial turfs have some technical drawbacks, among which a considerable superheating of the playing field in addition to environmental modifications with subsequent discomfort for the users. For avoiding the above described drawbacks combined systems have been proposed of mixed natural and artificial turf. A combined natural/artificial system is described in U.S. Pat. No. 6,145,248. It provides substantially a biodegradable substrate to which grass blades are connected of artificial material and onto which a layer is put of soil in which natural grass is sown. With time the roots of the grass expand and the biodegradable substrate disintegrates. Therefore, the roots reach the ground located underneath the substrate and radicate in it.
However, this solution is strictly bound to the availability of a ground and has strong applicative limits, because it cannot be used in case of surfaces where artificial turfs are usually installed.
Mixed turfs also exist, comprising both artificial fibres and natural fibres, i.e. plants, as described in WO2006008579 in the name of the same applicant. More precisely, such mixed turfs comprise a support of not biodegradable artificial material to which the fibres of artificial material are connected creating a synthetic turf. The synthetic turf, then, is filled with a loose infill material comprising different components, for example loose granules of rubber, plastic material, mineral material, organic material of vegetable origin, etc.
The loose infill material has in particular the function of keeping the fibres of artificial material substantially vertical. As above described, furthermore, the mixed turf comprises also natural fibres, i.e. plants, which can be put in the loose infill material through a sowing step, or a step of transplantation of plant portions belonging to at least one vegetable species that preform a quick vegetative development and give origin to a plurality of plants having roots arranged completely above the support.
Such mixed turf can be easily carried, rolled up, turned over, without fall of the loose infill material, and can be arranged in a desired moment on a desired support surface in such a way that can be immediately employed.
Other mixed turfs are described in KR100864276, in particular to provide mixed turf tiles.
However, the vegetable species that is present in the mixed turfs, as above described, can be subject to lack of water stress, owing mainly to the presence of the loose infill material that is highly draining and causes a quick outflow of irrigation water, dehydrating the plants of the vegetable species.
On the other hand, a too much frequent irrigation in the hot periods limits the use of the turf and causes dispersion of nutritive substances, and pollution of the underground.